A blog about butterfly and moth recording in Fife, Scotland

Rearing Butterfly and Moth Caterpillars

Sometimes, the best way to identify butterfly and moth species by caterpillar is to rear them, and that’s something I’ve decided to have a go at.

I’ll point out that I’m in no way an expert on this topic – far from it. I’m about as novice as they get! Most of the information I have has come from internet sources or from friends who have tried before. I have to admit, I wasn’t really surprised to find that more often than not, it’s not quite as simple as sticking a caterpillar in a jam jar with some leaves!

My first attempt was with a large green caterpillar, which was feeding on the climbing rose outside my house. It started off as a small (15mm) green caterpillar, and at the end was the 35-40mm monster seen below!

Now, I’m not sure which species it was… although one that certainly is a possibility is Beautiful Golden Y. Sadly, because the attempt failed, I’ll most likely never know (although if anyone out there does know, based on this photo, please do let me know!)

Why did the attempt fail? Well, in hindsight, that’s quite easy to explain. In this case, it was the wrong container used. The container I had used didn’t have enough ventilation, and condensation built up. Basically, the humidity levels were too high. As soon as the caterpillar had a poo, it started to go mouldy… and I simply wasn’t quick enough to clean up after it (though I did try!).

I’ve now learned from my previous mistake and I am working on my second attempt. To fix the problem with the container, I’m now using a Herp Haven, size Small to rear my caterpillar in. In honesty, for a single caterpillar, it’s probably a bit on the big side. I think in future I’ll purchase size Mini, which is only a little smaller, but substantially cheaper! I’ll leave the size small ones for rearing multiple caterpillars.

Here’s a photo of the current setup:

Now, before we discuss the contents of the container, I guess it’s time to discuss the requirements of the caterpillars. There’s only a couple of simple rules, really.

The first is that you should feed the caterpillar on the same plant species that you found it on. If you found it in a Hawthorn bush, feed it Hawthorn. Logical, really. If they’re not given the right food, they won’t eat and will starve.

Make sure the plants are fresh. If you can, put them in a small container of water so that they keep longer (though cover the container, so that the caterpillar can’t fall in and drown!)

Now, on to pupation. Different species pupate in different ways. Some species will bury themselves a little under the ground, some will wrap themselves up in the leaves of a plant, some need something to hang off of, and some build cocoons onto the bark of a tree. If you don’t know which species you have, how to you provide the right conditions? It’s simple, really… you provide them all! The caterpillar will do what comes naturally to it, as long as it’s got the option.

Now… my latest caterpillar. After all, there would be no point setting up the small tank if I don’t have something to put in it!

I was recently doing my Lantra Brushcutter Course, and in the course of cutting back some scrub, I found this little thing (though admittedly, it was a bit smaller than it is now… it’s currently about 25mm.).

Now, I’d just been cutting things down, and it certainly didn’t seem to be on any particular foodplant, so what do I feed it?! Nearby, there was Dock, nettle, bramble, hawthorn and a variety of grasses and any one of them could be the right source of food. As you’ll probably have guessed, if you’ve studied the photos and know plants at all… its weapon of choice is Dock leaves.

Now… the only reason I know this is because I emailed a photo of the caterpillar to my county recorder for ID. His tentative ID is that this is a Lesser Yellow Underwing caterpillar, and he suggested Dock or Hawthorn as the foodplant. To determine which one, I had to provide both. It was simply a case of waiting till the next morning (it’s a nocturnal caterpillar) to see which one it would eat. If you find yourself in a similar situation, grab some of every nearby plant species to find out which one it will eat.

Hopefully, this one will pupate in the next week or two (It should pupate in the soil) and a few weeks later we’ll have a new moth to play with.

Now… onto the moths themselves. Another little rule here. Most moths need a plant or the like to climb up on to stretch their wings once they’ve newly emerged. They’ll also need some space. Unless you happen to be watching the emergence as it happens, there’s a good chance that you’re going to want something larger than these tanks. I’ve not yet got to this stage, but I’ve purchased a pop-up rearing cage for when I do.

In interesting developments, I recently hosted National Moth Night at Cullaloe Local Nature Reserve, and I chose to take a couple of captured moths home to take photos of. In two of my containers, the moths had laid eggs! I now have eggs of Early Thorn (below) and White Ermine, so in the next 10 days or so, I’ll be getting to try my hand at rearing caterpillars on a grand scale! I suspect I may need a good few tanks for this, as all the records I’ve seen suggest that the caterpillars need to be separated into gradually smaller groups as they grow – I’ve got just under 40 eggs of both species. Assuming I can have a maximum of 5 per tub at the later stages, that still means I need 8 tanks! I think it will be worth it, though, to see the entire process of metamorphosis

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Interesting post Grahame.
I usually rear/feed any caterpillars in small tupperware pots, which i clean daily of any frass and only release them into the rearing tank when they look ready to pupate. Keeping them in smallish tubs, i find it easier to feed them.

I suspect it wrapped itself in the leaf in preparation of pupation. Several species like to do this (My own Early Thorn caterpillars have done this). As for why it would shake uncontrollably, I have no idea… hopefully one of the other visitors to the blog will be able to answer that one.